The present invention relates generally to wheel balancing machines used by tire shops and motor vehicle repair shops to perform off-vehicle balancing of automobile and truck tire and wheel assemblies. More specifically, this invention relates to a motorized electronic wheel balancer which is capable of operating at varying speeds of rotation and that has additional operator interface features that allow a user of the balancer to operate it with greater safety and efficiency.
In a conventional electronic wheel balancer, the tire and wheel assembly to be balanced is removed from the vehicle and placed on a shaft that extends laterally from the wheel balancer chassis. The shaft is directly or indirectly coupled to an electric drive motor so that the shaft as well as the tire and wheel assembly can be rotated to a predetermined speed. Once the wheel and tire assembly has been rotated to the predetermined speed, imbalance force transducers mechanically linked to the shaft and motor send electrical signals to a processor which are responsive to mechanical imbalances in the tire and wheel assembly. After these signals are processed, visual indicators are typically provided to the operator, identifying an amount of compensating weight that should be added to the tire and wheel assembly, as well as identifying a location or locations where correction weights should be attached.
In such wheel balancing machines, it is often desirable to operate the balancer at multiple shaft speeds. For example, it would be preferable to rotate the shaft at a slower speed for large wheels having high inertia as well as to operate at a higher speed for smaller wheels with lower inertia. This prevents overheating of the balancer drive motor on large wheels and improves the cycle time and signal to noise ratio in the collection of imbalance data for smaller wheels.
Another basis for operating the balancer at varying speeds would be to allow the operator to select a speed at which he wished to balance the wheel. Under these circumstances, the operator would select the speed. Then, as the shaft accelerated, the forces being generated by the imbalance in the tire and wheel assembly would be monitored. If the imbalance forces generated were low enough to allow for safe operation at the selected speed, the shaft would be accelerated to the desired speed and the imbalance measurement made. However, if excessive imbalance forces were detected, the power would be removed from the drive motor at a safe speed and the measurements made at that speed.
Finally, variable speed operation is also desirable to allow the operator to rotate the tire and wheel assembly at a speed low enough to permit visual inspection of the rotating tire. For safety reasons, Underwriters Laboratories requires that if the tire and wheel assembly is rotated at or above specified speed, the assembly must be covered by a protective hood. Thus, the safety hood, which ordinarily covers the assembly for the protection of the operator, must be in its upward position to allow for visual inspection of the wheel runout or other aberrant conditions that must be visually detected. After the operator has completed the runout inspection, he could stop the drive motor or lower the hood and the balancer could then be accelerated to a higher speed to conduct a normal imbalance measurement.
Another important characteristic of an electronic wheel balancer is to quickly and effectively display to the operator the precise locations for placement of the compensating weights. In the prior art, this is has been accomplished by various combinations of display or illumination devices on a display panel mounted to the balancer. One problem associated with the prior art display panels in a multi-planed electronic wheel balancer is the relationship between weight placement and the multiple correction planes that can be selected in balancing a tire and wheel assembly. In the typical microprocessor based electronic wheel balancer, the imbalance in a wheel is resolved into two correction planes. In the variety of vehicle wheels that can be used, there are many different correction planes where corrective weights can be applied, with five of such planes shown in FIG. 6. The operator ordinarily will select the weight placement planes in advance, based on several factors. The processor of the balancer will use this information, along with the imbalance force measurements, to calculate weight placement locations. In the prior art user interface and display panels, the steps of operator selection of the correction planes (by use of a selection key or button) and visualization of weight placement can be confusing because of poor arrangement of the buttons and display.
In balancing a standard steel wheel, knowing where on the wheel to apply the correction weights is straightforward. Clip weights are attached to the wheel rim at the required angular position as specified by the electronic wheel balancer display. The situation becomes more complicated if an alloy wheel is being balanced. It may be impossible to attach a clip weight to the rim of the wheel or the vehicle owner may want the weights to be hidden from view. In those situations, one or both weights may be placed on the interior of the wheel when performing a dynamic balance. The weights may be a combination of clip weights and tape weights or both may be tape weights.
Various methods have been tried in the prior art to allow the operator to select the weight location, all of which have had some drawbacks. One method has been to provide selectable icons on the operator interface panel, each of which represents a specific wheel configuration as well as corresponding weight locations. Another method has been to have a graphic display and a series of switches on the operator panel which allow selection of fixed groupings of weight locations. Both of these methods suffer from inflexibility and are not user friendly.
What is needed, then, is an electronic wheel balancer that can be safely operated at variable speeds for different sized wheels. An electronic wheel balancer is also needed that has an improved operator interface panel to make it easier and less confusing to coordinate the selection of correction planes with visualization of weight placement location.